Generally, an electrode assembly of batteries comprises a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The separator is designed to be larger than the positive and negative electrodes to prevent a short circuit between the negative and positive electrodes. A nonwoven fabric made of a polyamide resin such as a nylon material or a polyolefin resin such as a polypropylene material has been used for the separator.
However, the use of the above materials for the separator has drawbacks. Namely, the separator using the nonwoven fabric made of nylon material may, when used in a nickel-metalhydride battery, cause charge retention of the battery to deteriorate. That is, NH.sub.4- of the nylon causes the battery to self-discharge. As a result, the separator using the nonwoven fabric made of polypropylene material has to go through a complicated hydrophilic treatment process.
In addition, separators made of the above two materials cannot provide sufficient electrolyte-retaining power.